Algorithmic Approach to Diagnosis of Hydatidiform Moles Possible Hydatidiform Mole p57 immunohistochemistry Negative p57 (villous stroma, cytotrophoblast) Positive p57 (villous stroma, cytotrophoblast) Morphology appropriate Morphology equivocal Molecular genotyping Androgenetic diploidy Diandric triploidy Biparental diploidy CHM or eCHM PHM Non-molar

Supplemental figure legend: Algorithmic approach to diagnosis of hydatidiform moles. Potential molar cases are first triaged with p57 immunohistochemistry. If p57 is negative and morphology is appropriate, a diagnosis of complete hydatidiform mole (CHM) or early complete hydatidiform mole (eCHM) can be rendered. If p57 is positive, molecular genotyping is performed (regardless of morphology). The subtypes of molar specimens, including CHMs and partial hydatidiform moles (PHM) are distinguished from non-molar specimens by the specific genotyping results indicated.